1. Field of the Invention
The invention relates to rotary noise attenuating valves, and particularly to a noise attenuating valve which includes an impedance assembly of the type previously limited to use with linear valves, with an interface or feeder assembly provided to allow the use of the impedance assembly with a rotary valve, such as a ball valve. The invention also relates to noise attenuating valves in which the impedance assembly is mounted within the valve housing, either downstream of the closure member or mounted for movement with closure member.
2. Discussion of Background
FIG. 1 shows a conventional linear valve assembly with a noise attenuation or impedance assembly. This valve is also known as a drag valve. As shown in FIG. 1, the linear valve includes an actuator assembly 10 for moving a piston 12. Disposed about the piston is an impedance assembly 14 which includes a plurality of passageways 16 extending therethrough. When the piston 12 is in the lowermost position, none of the passageways 16 is exposed to the incoming flow I. As the piston is opened (i.e., moved upwardly in the drawing figure) flow passes through the passageways 16 to provide an exit flow E, with the amount of flow varied by the position of the piston 12, which in turn varies the area or proportion of the impedance assembly which is exposed to the incoming flow.
The arrangement shown in FIG. 1 is particularly advantageous from a standpoint of reducing noise and, from a noise reduction standpoint, is superior to that available for rotary valves. However, the conventional arrangement is limited, for example, with regard to the size for which such an arrangement can be practically manufactured. For example, with piston diameters D larger than twelve inches, the arrangement is excessively expensive and can encounter instability problems.